# CVE-2026-102560: libsoup heap buffer overflow in permessage-deflate WebSocket extension

Source: https://junglewise.ai/threats/cve-2026-102560-a-flaw-was-found-in-libsoup-when-the-permessage-deflate  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-29. Updated: 2026-09-29  
License: CC BY 4.0 with a link back

CVE-2026-102560 · Severity: high · CVSS 8.6 · Published 2026-09-29

libsoup is a networking library used by web applications and services to handle HTTP and WebSocket communications. When compressing very large WebSocket messages with the permessage-deflate extension enabled, a calculation error causes the library to write beyond allocated memory, allowing attackers to crash the application or potentially read sensitive data. This affects applications that accept untrusted or unbounded WebSocket messages.

Technologies: [Gnome Libsoup](https://junglewise.ai/threats/technologies/libsoup). Vendors: [Gnome](https://junglewise.ai/threats/vendors/gnome).

## Quick answers

**Is CVE-2026-102560 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-102560 being exploited in the wild.

**How severe is CVE-2026-102560?** High severity, with a CVSS score of 8.6, published 29 September 2026.

**Which products and versions are affected?** Gnome Libsoup affected versions not specified in advisory.

**Is there a fix for CVE-2026-102560?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-102560 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-102560?** Check whether you run Gnome Libsoup at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability is a heap buffer overflow in libsoup's WebSocket permessage-deflate extension handler, triggered when size calculations for GByteArray growth wrap due to compression of very large outgoing messages, allowing zlib to write past the buffer boundary. The attack requires network access and exploitation of the permessage-deflate extension negotiation with a crafted large message payload; no authentication or user interaction is needed. An attacker can achieve heap corruption, information disclosure (including memory addresses and cryptographic keys), or denial of service.

## Affected products

- GNOME libsoup affected versions not specified in advisory

## Timeline

- 2026-09-29: disclosed

## References

- [https://access.redhat.com/downloads/content/package-browser/](https://access.redhat.com/downloads/content/package-browser/)
- [https://access.redhat.com/security/cve/CVE-2026-102560](https://access.redhat.com/security/cve/CVE-2026-102560)

## Related threats

- [libsoup HTTP request smuggling via undrained Expect: 100-continue body](https://junglewise.ai/threats/cve-2026-103399-a-flaw-was-found-in-soupserver-libsoup-when-an-http-1-x-client)
- [libsoup heap buffer overflow in WebSocket handling](https://junglewise.ai/threats/cve-2026-102558-a-flaw-was-found-in-libsoup-when-max-incoming-payload-size-is)
- [libsoup out-of-bounds read in data-URI base64 decoding](https://junglewise.ai/threats/cve-2026-102555-a-flaw-was-found-in-libsoup-the-soup-uri-decode-data-uri)
- [libsoup heap corruption in WebSocket message reassembly](https://junglewise.ai/threats/cve-2026-102557-a-flaw-was-found-in-libsoup-when-reassembling-fragmented)
- [libsoup type confusion in WebSocket Pong signal](https://junglewise.ai/threats/cve-2026-102556-a-flaw-was-found-in-libsoup-when-handling-an-incoming-websocket)